1. Field of the Invention
The present invention relates generally to plasma arc reactors and systems and, more particularly, to a modular plasma arc reactor and system as well as related methods of creating a plasma arc.
2. State of the Art
Plasma is generally defined as a collection of charged particles containing about equal numbers of positive ions and electrons and exhibiting some properties of a gas but differing from a gas in being a good conductor of electricity and in being affected by a magnetic field. A plasma may be generated, for example, by passing a gas through an electric arc. The electric arc will rapidly heat the gas by resistive and radiative heating to very high temperatures within microseconds of the gas passing through the arc. Essentially any gas may be used to produce a plasma in such a manner. Thus, inert or neutral gasses (e.g., argon, helium, neon or nitrogen) may be used, reductive gasses (e.g., hydrogen, methane, ammonia or carbon monoxide) may be used, or oxidative gasses (e.g., oxygen or carbon dioxide) may be used depending on the process in which the plasma is to be utilized.
Plasma generators, including those used in conjunction with, for example, plasma torches, plasma jets and plasma arc reactors, generally create an electric discharge in a working gas to create the plasma. Plasma generators have been formed as direct current (DC) generators, alternating current (AC) plasma generators, as radio frequency (RF) plasma generators and as microwave (MW) plasma generators. Plasmas generated with RF or MW sources are called inductively coupled plasmas. For example, an RF-type plasma generator includes an RF source and an induction coil surrounding a working gas. The RF signal sent from the source to the induction coil results in the ionization of the working gas by induction coupling to produce a plasma. DC- and AC-type generators may include two or more electrodes (e.g., an anode and cathode) with a voltage differential defined therebetween. An arc may be formed between the electrodes to heat and ionize the surrounding gas such that the gas obtains a plasma state. The resulting plasma may then be used for a specified process application.
For example, plasma jets may be used for the precise cutting or shaping of a component; plasma torches may be used in applying a material coating to a substrate or other component; and plasma reactors may be used for the high-temperature heating of material compounds to accommodate the chemical or material processing thereof. Such chemical and material processing may include the reduction and decomposition of hazardous materials. In other applications plasma reactors have been utilized to assist in the extraction of a desired material, such as a metal or metal alloy, from a compound which contains the desired material.
Exemplary processes which utilize plasma-type reactors are disclosed in U.S. Pat. Nos. 5,935,293 and RE37,853, both issued to Detering et al. and assigned to the assignee of the present invention, the disclosures of each of these patents are incorporated by reference herein in their entireties. The processes set forth in the Detering patents include the heating of one or more reactants by means of, for example, a plasma torch to form from the reactants a thermodynamically stable high temperature stream containing a desired end product. The gaseous stream is rapidly quenched, such as by expansion of the gas, in order to obtain the desired end products without experiencing back reactions within the gaseous stream.
In one embodiment, the desired end product may include acetylene and the reactants may include methane and hydrogen. In another embodiment, the desired end product may include a metal, metal oxide or metal alloy and the reactant may include a specified metallic compound. However, as recognized by the Detering patents, gases and liquids are the preferred forms of reactants since solids tend to vaporize too slowly for chemical reactions to occur in the rapidly flowing plasma gas before the gas cools. If solids are used in plasma chemical processes, such solids ideally have high vapor pressures at relatively low temperatures. However, these type of solids are severely limited.
As noted above, process applications utilizing plasma generators are often specialized and, therefore, the associated plasma jets, torches and/or reactors need to be designed and configured according to highly specific criteria. Such specialized designs often result in a device which is limited in its usefulness. In other words, a plasma generator which is configured to process a specific type of material using a specified working gas to form the plasma is not likely to be suitable for use in other processes wherein a different working gas may be required, wherein the plasma is required to exhibit a substantially different temperature or wherein a larger or smaller volume of plasma is desired to be produced.
In view of the shortcomings in the art, it would be advantageous to provide a plasma generator and associated system which provides improved flexibility regarding the types of applications in which the plasma generator may be utilized. For example, it would be advantageous to provide a plasma generator and system which enables the direct processing of solid materials without the need to vaporize the solid materials prior to their introduction into the plasma. It would further be advantageous to provide a plasma generator and associated system which produces an improved arc and associated plasma column or volume wherein the arc and plasma volume may be easily adjusted and defined so as to provide a plasma with optimized characteristics and parameters according to an intended process for which the plasma is being generated.